Air filtration



1957 F. w. YOUNG ,815,826

AIR FILTRATION Filed May 5, 1955 \a I" I g 3 l -I n lh li I I I F: I'l I co i m V K g, INVENTOR. FRANK W. YOUNG States This invention relates to cleaning of gases and more particularly relates to a novel method and apparatus for continuously and very etficiently separating entrained particles from a gaseous mixture passing through-a conduit.

One object of the invention is to provide an improved method of and apparatus for separating particles from a traveling stream ofgas.

Another object of the invention is to provide such an improved method of and apparatus for gas cleaning in which the particles are filtered from the gas onto a traveling mat or web forming a filter medium which is passed across the path of travel of the gas.

Still another object of the invention is to provide s'uch a method and apparatus in which the web or mat forming the filter medium is formed continuously from a bath containing a mixture of liquid and filter material and in which, after passage across the path of travel of the gases, the web is disintegrated into its components, these components washed and then returned to the original bath to be reused in the formation of the web.

Yet another object is to provide such a method and apparatus permitting the formation of the filtering web or mat from inert fibrous material which will be nonreactive with the components of the gaseous stream being cleaned.

In accordance with the invention I continuously form a web of fibers from a bathcontaining a mixture of filter material and liquid. This formation may most conveniently be carried out on the surface of a continuous rotary vacuum filter which may be of a conventional type. The web is formed by depositing the material in an endless open-work support or belt which passes around a portion of the periphery of the filter and then across the stream of gases to be cleaned and back to the filter drum. The filter material becomes matted and embedded in the belt to form the traveling web. The web after it is formed may be dried, if necessary, by a current of dry warm air or otherwise and then when it is led across the path of travel of the gaseous mixture to be cleaned, the gases will pass through it and the particles be captured and deposited on the filter material of which the web is composed. Preferably, I lead the web around a .roll and return it in such a way that it passes twice through the gas duct, this being possible in view of the fact that the web is firmly matted in the supporting belt and does not merely rest on the surface thereof. Thereupon, I disintegrate the web and separate the dirt by washing the material fro-m the supporting belt. The filter material is then returned to a make-up tank to which may be addedadditional material and fresh liquid as needed and the mixture returned to the original bath so that the material may be reused in again forming (the web. The

dirt collected forms a sludge which can be removed periodically or continuously from the bottom of the makeup tank, or otherwise.

The material of which the endless belt or support is composed and the particular material forming the filter- ,tefit he 2,815,826 Patented Dec. 10, 1957 ing web are chosen so as to benonreact'ive with chemicals which maybe carried by the gaseous mixture. This is especially important .if the gases to be cleaned are at high temperatures, of 1000' F., for example, such ;as in the stacks of blast furnaces and open hearth furnaces, or the like. In such installations I prefer to employ a stainless steel belt and I deposit on "it as filter material fibers of rock wool, glass wool, slag woo'l, etc., the 'web and the chain belt being thoroughly driedbe'fore encountering the gaseous mixture to reduce any corrosiveeffect.

Still further objects, features and advantages of their!- venti'on will become apparent from the following detailed description of presently preferred apparatus for practicing the same, taken in conjunction with "the accompanying drawings in which like "parts are indicated by like numerals in the several views and in which:

Fig. l is a schematic representation-eta complete'installation for the cleaning of flue gases according to the invention;

Fig. 2 is a fragmentary cross-sectional view on "line 22 of Fig. 3 showing the construction of one form'o'f endless chain belt which may be employed in the system shown in Fig. 1; and

Fig. 3 is a plan view of the belt, illustrating the special arrangement which insures good trackingof the traveling belt.

As seen in the drawings, a duct, such as a flue or stack of ablast furnace or open hearth furnace, through'which passes a stream of gases to be cleaned, "is indicated generally'by the numeral 10. On one side of this duct 10 is mounted a tank 12 adapted to contain a bath comprising a liquid suspension of the material which has been selected as suitable to make up the filtering "web. Mounted for rotation about ahorizontal axis and partially submerged in the bathcontained in the tank 12 is a continuous rotary vacuum filter drum indicated generally by the numeral 14. Rotary drum vacuum filters are well-known (see, for example, U. S. Patent No. 2,352,303), and, therefore, I will not describe the construction and operation of the filter in detail, except to indicate certain advantageous arrangements which should be employed to obtain optimum results in accordance with the invention.

The rotary'filter may comprise a cylindrical drum 16 which is perforated throughout bya series of ports 18 and carries a filter cloth l9 onits surface. Entering the drum, as through a trunnion 17 at one end'th'ereof, isa filtrate pipe 26 which is preferably of reasonably large diameter since it also serves to evacuate air as welllas liquid from the interior of the drum through openings 2%. Arranged to be carried on the surface of the drum 16 resting directly on the filter medium 19 *is an endless chain belt 22 which, in the particular'embodiment shown, may also serve as a drive for rotating the drum. As best seen in the fragmentary views of Figs. 2zand3, this link or chain belt 22 is preferably made up .of a series of sections of metallic links 21, the sections being joined to each other by rods 23. The :'links in adjacent sections alternate in being turned first right-hand and next :lefthand, and the sections themselves may be,.-for example, conveniently about two feet in length each. By thus alternating the direction of the links fromsection .tosection, I insure that the belt will track properly on the rolls and drum.

Approximately fifty percent of the drum surface is sealed off against air leakage and filtration by an internal shoe 24 mounted on spokes 26 whichmay be supported on the pipe 20 or axle of the drum, or in any suitable tothe output of a pump 30, .the'input side 3'2 ofwhitth communicates with the make-up tank 34. The liquid level ofth'e bath contained in the tank 12 is maintained constant by an overflow pipe 36 which conducts any overflow suspension back into the make-up tank 34.

Fresh filter material such as suitable fibers, as needed, are supplied to the tank 34 from a hopper 38 through a conduit 40, the flow being controlled by a valve or damper 42 so that the mixture in the tank 34 will have the proper consistency. The fibers are uniformly distributed in the liquid by the action of an impeller 44. The tank 34 has an outlet 46 and a liquid inlet 48 for purposes which are hereinafter more completely explained.

The spiral wire belt 22 is led onto the periphery of the drum 16 over a guide roll 50 just before the drum surface submerges in the bath on downside. The belt then passes throughthe bath, re-emerges from the same, after becoming matted with the filter material which forms a web, as hereinafter explained, and is led off the drum at a point approximately 270 from the point of beginning. The belt and web then pass through an opening 52 in the duct or flue 10, across the path of travel of the gases, as indicated by arrows, and out another opening 54.. The belt and web then pass around a roll 56, which may be driven byany suitable means, reverses its direction and passes back across the stack through openings 53 and 60. After leaving the opening 60, the belt passes through a casing 62 which is divided by an internal partition 64 into two chambers, for washing purposes, as hereinafter explained, thence about a guide roll 66 to the point of beginning.

The outlet pipe serves to exhaust air and filtered liq- .uid which rises above the open end of the pipe 20 from the interior of the drum 16. This pipe operates as a barometric leg to draw air and liquid and discharge into another tank 72, the lower end of the pipe 20 being below the liquid level of the tank 72. A pressure differential is thus created which forces liquid and air from the exterior of the drum 16 through the belt 22, filter cloth 19 and ports 18 on the ascending side of the drum, thus building up a mat or cake of filter material in the open-Work belt.

Arranged through an arc of approximately 90 opposite the surface of the drum 16 on the up side thereof, I provide optionally a bank of infra-red heating lamps 74. This portion of the surface of the drum is enclosed, at least in part, by a hood 76 thus forming a drying chamber for the web which is formed on the endless belt. Discharging into this drying chamber is the outlet of an air heater 78 through which air is drawn by the pressure differential above mentioned. These fibers will quickly form a mat or web entangled with and firmly held by the links of the chain. I have found in general, that the thickness of the web or pad will be determined by the thickness of the chain belt in which it is deposited. Furthermore, the stock may be very free-flowing and even during the relatively small arc wherein filtration occurs will build up into a web of required thickness very rapidly. Even with stock having a consistency of about .l% to about .25%, with a belt speed of about one inch per minute a web two inches thick may be easily produced. With such consistencies and at such speed, the filtrate will pass through the belt, filter cloth and filter drum at about 1,000 gallons per minute. This means that the pipe 20 must have a diameter such as to produce and handle such a great flow. For example, a pipe of the diameter of twelve inches arranged so that there is a reasonable head between the liquid level within the filter drum 16 and that in the tank 72 will be found entirely suitable to induce and carry a flow of this magnitude as well as to suck air through the heater and into the drum in desired volume.

The web formed in this manner will then, after emergence from the bath, be rapidly and thoroughly dried by the action of the hot air provided by the heater 78, the

drying action being accelerated by radiant heat from the lamps 74, if desired. The thoroughly dried web then passes through the opening 52, across the flue 10, around the drive roll 56, again through the flue, passing in through the opening 58 and out through the opening 60 to the first Washing in the tank 62. The web being deposited in and reinforced by the links of the belt 22 will undergo this reversal without injury. The first wash is provided by a sprayer 82 fed with filtrate liquid from the tank 72 by means of pipes 84 and 86 and pump 88. Liquid discharged by the sprayer 82 will largely disintegrate the fibrous web, causing the fibers and the entrained particles, picked up thereby during passage through the stack, to drop to the bottom of the tank 62 from whence they will drain to the make-up tank 34. The chain and any remaining entangled fibers then pass through an opening in i the partition 64 to be washed again by a spray 90 of clean fresh liquid supplied from a main 92 and controlled by a valve 94. This second washing serves completely to clean the chain belt so that it will be ready for the redeposit therein of the fibrous web when it again passes through the bath in the tank 12.

I have found that a suitable filtering web may be formed very rapidly using a free filtering suspension of fibers in liquid. It is for this reason I preferably seal off a substantial portion of the submerged area of the filter drum to prevent the web from becoming too thick prior to emergence from the bath. The consistency of the fibrous mixture used, the speed of travel of the belt 22, the amount of heat and air required for drying, etc., may all be adjusted by engineers skilled in the art to meet the requirements of any particular installation. Where the gases to be cleaned do not contain corrosive chemicals, and very high temperatures are not involved, the step of completely drying the web prior to use in cleaning the gas may be unnecessary or, indeed, undesirable, for a moist web may in some cases clean the gas more effectively. Dirt particles captured by the web from the gaseous vehicle and washed off by the sprays into the tank 62 pass with the fibers through the pipe 48 back into the make-up tank 34. This tank is preferably provided with a bottom having sloping sides so that the dirt will collect in the form of a sludge in the very bottom of the tank. This sludge may be cleaned out periodically by opening the valve 46. It is evident that these particles may be separated in any other suitable manner.

The particular filter material employed will, of course, be chosen with reference to the conditions of operation, including the chemical composition, temperature, and other characteristics of the gas to be cleaned. For blast and open-hearth furnace gases, a mineral slag wool has been found suitable. Other inert materials may also be used for hot gases, including rock wool, glass wool, etc. These materials when formed into a filtering pad or web on the spiral wire belt will be found to remove substantially percent of the dirt from the flue gas, and this is an important accomplishment in an industry where pollution of the atmosphere is such a serious problem. When operating on gases which contain appreciable quantities of sulfur, or other chemicals capable of forming corrosive solutions with water, it is essential that the fibers and belt be completely dry before the web is advanced through the flue to prevent formation with the moisture of corrosive compounds, such as sulfuric acid, which would attack the steel wire belt. For these purposes the drying system must be made completely adequate and engineers skilled in the art will have no difliculty in establishing the requisite characteristics for a particular installation.

It will be evident also that the liquid levels in the various tanks may be controlled by suitable float valves or otherwise, and that various automatic control devices well known in the art of filtration may be utilized to make the practice of the invention as nearly fully atuomatic as may be.

It is clear that the invention may be practiced utilizing other components and structures than those specifically herein disclosed and described, that the nature of the construction materials and filter materials may be varied to meet the requirements of particular installations, and that other modifications, adaptations and rearrangements, nevertheless Within the scope of the invention, will occur to those skilled in the art. Therefore, the invention is not limited to the specific arrangements and details of the preferred embodiment illustrated in the drawings and herein described, but only by the scope of the appended claims.

I claim:

1. The method of continuously separating particles from a gaseous vehicle which comprises firmly matting a relatively thick fibrous web of filter material in a traveling open-work carrying medium moving through an endless path by forcing liquid carrying such material through said medium as the latter passes through a bath in a portion of said path, passing the web thus formed and said medium through another portion of said path in at least one direction across a stream of gas carrying the particles to be separated so as to filter out said particles, washing both said material and the entrained particles from said medium as the latter passes through still a third portion of said path, and thereafter returning the clean medium to the point of beginning for reuse.

2. The method as claimed in claim 1 which includes the steps of separating said material from said particles after both have been washed from said medium and returning the separated clean material to the bath to be used again in the practice of said method.

3. The method as claimed in claim 2 which includes the step of drying the web prior to passing the same through said stream.

4. Apparatus for continuously separating particles from a gaseous vehicle moving as a stream through a conduit, which comprises the combination with said conduit of an endless gas and liquid permeable belt, supporting and driving means for moving said belt through a predetermined closed path during at least one portion of which it passes across said conduit, and during another portion of which in advance of said first-named portion it passes through a bath adapted to contain a mixture of liquid and fibers, and during a third portion of which it passes through a washing zone, means for forcing liquid through said belt while passing through said bath to embed a relatively thick and durable mat of said fibers therein, means arranged in said washing Zone for washing said fibers and any particles deposited thereon from said belt after the latter has passed across said conduit, and means for thereafter separating said particles from said fibers and returning the latter to said bath.

References Cited in the file of this patent UNITED STATES PATENTS 140,034 Goodfellow et al June 17, 1873 1,322,804 MacFadden Nov. 25, 1919 1,472,574 Wright et a1 Oct. 30, 1923 1,995,378 Dahlman Mar. 26, 1935 2,152,900 Manning Apr. 4, 1939 2,352,303 Young June 27, 1944 FOREIGN PATENTS 553,540 France Feb. 13, 1923 

